Short Circuit Data: transformer
Typical equipment impedances (%Z) and X/R ratios for short circuit calculations per IEEE 141 (Red Book) and IEEE 551 (Violet Book). Covers transformers by kVA, utility sources by voltage level, cables, motor contributions, generators, and reactors.
| equipment type | rating label | asym multiplier typical (dimensionless) | impedance pct max (%) | impedance pct min (%) | impedance pct typical (%) | mva base (MVA) | notes | xr ratio max (dimensionless) | xr ratio min (dimensionless) | xr ratio typical (dimensionless) |
|---|---|---|---|---|---|---|---|---|---|---|
| transformer | 10000KVA | 1.33 | 8 | 6 | 7 | 10 | Liquid-filled substation transformer | 35 | 18 | 25 |
| transformer | 1000KVA | 1.24 | 6 | 4.5 | 5.75 | 1 | Dry-type or liquid; dual-voltage primary | 10 | 6 | 7 |
| transformer | 112.5KVA | 1.15 | 5.75 | 1.5 | 3.1 | 0.1125 | Dry-type LV distribution; most common small commercial size | 4.5 | 2.5 | 3.5 |
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